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Old Aug 09, 2007, 01:31 AM
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Jim, when are you going to come out to the Basin with your test equipment?

Gene
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Old Aug 09, 2007, 08:49 AM
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Corpus Christi, Texas, United States
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Quote:
Originally Posted by K-Tonic
Jim, when are you going to come out to the Basin with your test equipment?

Gene
http://www.rcgroups.com/forums/showt...=9#post7955724

Post #131 has all the details.
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Old Aug 09, 2007, 09:50 AM
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I think it's just a trickle down effect from the "big boys". They don't someone offering a better product at a drastically lower price.
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Old Aug 14, 2007, 04:04 PM
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East Central Ohio, United States
Joined Jun 2004
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I wrote to AMA about this:

"I read on an RC forum that Xtremelink will be banned at a competition but Spektrum and JR will not. I guess some people had problems with XPS.

I just want you to know I have been flying XPS all summer with hundreds of flights with 5 receivers in 5 different planes without a single problem at all.

Please do not ban XPS at AMA events. If this happens I will be VERY disappointed.

Thank you."

I got this reply:

"Thank you for your question and input.

To the best of our knowledge there is no movement to "ban" xtremelin k operations at sanctioned events.

However, contest directors do the authority to configure events as they see fit so it is not impossble to have an event where just such a case exists. If that rule is instituted it must be published in advance of the event so everyone is aware of the change."

Guess there isn't much we can do, is there?
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Old Aug 18, 2007, 12:56 PM
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I was told by an old time cable guy that some of the worst interference they had came from ships entering and leaving costal harbors. He told me ships would be transmitting on illigal freqs and with very high power. He was wondering if that could be the case as the basin may not be very far from the harbor area.

Just a thought. Cheers
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Old Aug 18, 2007, 10:34 PM
Dick Corby
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Enumclaw, Washington
Joined Sep 2004
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Quote:
Originally Posted by Foamaholic
I got this reply:

"Thank you for your question and input.

To the best of our knowledge there is no movement to "ban" xtremelin k operations at sanctioned events.

However, contest directors do the authority to configure events as they see fit so it is not impossble to have an event where just such a case exists. If that rule is instituted it must be published in advance of the event so everyone is aware of the change."

Guess there isn't much we can do, is there?
Being a Contest Director, and Active in the Heirarchy of my club, yes there is something we can do.

Most clubs depend on the income from contests and other activities they may conduct over the period of a year. If I were to have a contest, and banned a given system, it would of course reduce the participation and therefore the income an event needs to generate.

As XPS gets more press, and users, this will automatically become a non-issue. As it stands now in our club there are about 4 XPS systems in use. Those using it are so pleased that others are trying to get on the same system. As supply catches up with demand, this will increase. So in time XPS will be have a presence that will make it a no-win situation to ban it.
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Old Aug 18, 2007, 11:37 PM
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Glad to hear that. Hope it turns out that way. I am just concerned that it might spread and others may think XPS is no good and should be banned, which is NOT the case.
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Old Aug 24, 2007, 08:04 AM
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This is very basic question. On the XPS web site, they boast that the system is FHSS. But it changes frequency when it encounter some interference. Does this mean if XPS is interefered by Spektrum of DSSS the XPS shifts the frequency?
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Old Aug 24, 2007, 08:11 AM
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XPS is DSSS with on-demand channel change when the background noise gets too high. The XPS currently is the only fully bidirectional system. The Rx ACKs every packet and reports information about packet loss and noise level to the Tx. At any time either the Rx or Tx can initiate a hop to an alternate channel to find a cleaner connection. The details of the hopping algorithm are proprietary but the concept is straightforward.
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Old Aug 24, 2007, 08:11 AM
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The XPS system is a hybrid, it is DSSS but also has the ability to change frequencies if the noise floor raises to unacceptable levels. As far as Spektrum interfering, it wont. Jim had posted a screen shot of a spectrum analyzer where a DX6 system was parked right on top of an Xtremelink and neither was affected. Which is as it should be according to FCC regs.
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Old Aug 25, 2007, 10:05 AM
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Quote:
Originally Posted by chrisf testpilot
The XPS system is a hybrid, it is DSSS but also has the ability to change frequencies if the noise floor raises to unacceptable levels. As far as Spektrum interfering, it wont. Jim had posted a screen shot of a spectrum analyzer where a DX6 system was parked right on top of an Xtremelink and neither was affected. Which is as it should be according to FCC regs.
Is this really true? When the two systems on same frequency, there may be some signal loss for each system. Of course there might be some difference in RF emission timing. However, I guess that they don't see any RF timing of other's. Because if they see each other and give up to output RF then it results in lock-out. I saw in some thread that says the XPS's bandwidth is around 5MHz(?). For example, if Spektrum occupy 3 continuous bands and XPS use the center of these 3 frequencies, does the XPS shift the frequency?Does anybody know how the XPS act under this condition?
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Old Aug 25, 2007, 10:34 AM
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Radi you need to do some reading about spread spectrum technology. Many systems can be transmitting simultaneously on the same logical channels and still work just fine.

For the 2.4GHz IMS band there are no defined channels and each spread-spectrum implementation divides the band up into logical channels differently. Spektrum divide it into 80 x 1MHz logical channels and each Tx/Rx link uses two channels. Other Spektrum radios will look for what they consider to be idle logical channels before establishing a link.

XPS uses MaxStream technology which divides the band into 12 to 16 x 5MHz logical channels. It uses a single logical channel for each Tx/Rx link. The choice of a channel is based on the detected noise floor at the Rx at boot time. If the noise floor rises too fast or too far the Rx will negotiate with the Tx to change to a lower noise channel.

Both these systems, and Futaba's FASST which they claim is true FHSS, can all coexist without any problem. At some point when there are dozens or maybe hundreds of systems all operating at the same location the overall noise floor will get high enough to affect packet loss rates leading to sluggish control performance and ultimately link failure. It is worth noting that it is estimated that there were around 400-500 out of 750 registered pilots at the recent IRCHA event using spread spectrum radios including Spektrum (the majority), XPS and FASST. Since there was no requirement to impound spread spectrum Tx, these were all out there uncontrolled on the flightline, in the pits and in the carpark. At any one time there were bound to be dozens turned on, if not more, all without any problems.
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Old Aug 25, 2007, 11:24 AM
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Hi kgfly, thanks for the lecture. I also believe and hope that the each system can work without any problem in ISM band. But OTOH each system has to accept any interference from other system in 2.4GHz band based on the FCC ruling. Does this "accept" mean "give-up" or "avoid" the interference from others? Anyway, I think, ideally speaking, each system can co-exist without problems. But practically speaking, is this true? For data transmission like W-LAN, even if the system encounters some signal loss, then the system can still re-send the data. So in this case the data rate is slow down but it looks like the system works still fine. But for our RC application, this slow down result in slow latency or lock-out and the pilots can directly fell the issue. How does every body think? Am I still misunderstanding?
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Old Aug 25, 2007, 06:22 PM
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We tested 10 aircraft hard coded to the same 10 frequencies with no issues in latency. We are using about 400us of airtime for the transmission/ack. Total saturation would not occur until 2500 units (per frequency) were in use at the same time. Even then, spread spectrum encoding allows for simulataneous data, extrapolating the proper data from stream.
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Old Aug 25, 2007, 09:51 PM
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Quote:
Originally Posted by JimDrew
We tested 10 aircraft hard coded to the same 10 frequencies with no issues in latency. We are using about 400us of airtime for the transmission/ack. Total saturation would not occur until 2500 units (per frequency) were in use at the same time. Even then, spread spectrum encoding allows for simulataneous data, extrapolating the proper data from stream.
Thanks Jim. But is your explanation is based on the condition only with multi number of XPS on same frequency? I guess when thinking about co-exisiting with Spektrum the situation is comletely different. Guessing from the data rate of the Spektrum, their RF time is longer than XPS. Then is XPS be affected by Spektrum?
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